Coupling of aromatic hydroxy compounds



. COUPLING or AROMATIC HYDROXY COMPOUNDS Frank H. Seubold,. Jr., Frederick F. Rust, and William E. Vaughan, Berkeley, Cali!.,'assigi1or a to Shell Development Company, San Francisco, Calif., a corporation of Delaware v No Drawing. Application August 31,1948, SerialNo. 47,154 r v This invention relates to-a process for coupling aromatic hydroxy compounds such as phenols,

naphthols and poiyhydric aromatic compounds;

More particularly, the invention provides a process for forming carbon-to-carbon bonds between molecules of aromatic hydroxy compounds substantially without oxidizing the hydroxyl'groups.

Numerous polynuclear aromatic hydroxy'com pounds have been synthesized'or have been isolated from naturally occurring compositions. The polynuclear aromatic hydroxy compounds have proven to be of great value in the inhibition of oxidation, in the developing of photographs oxidation of the hydroxyl groups to carbonyl groups, i. e., the conversion of a phenol to a biphenoquinone. In spite'of the value of the polynuclear aromatic hydroxy compounds, methods of forming them by proceses other than the reduction of the biphenoq-uinones obtainable by the oxidative-coupling of phenols have heretofore involved an even more extensive series of reactions. For example, U. S. Patents 2,260,739 and 2,285,563 disclose the prepartion of binuclear aromatic hydroxy compounds by converting mononuclear hydroxy compounds to an ether by alkylation, converting the ether to an iodo derivative by the action of iodine andmercurlc oxide, coupling the substituted-ether molecules by splitting out iodine with copper and hydrolyzing the binuclear ether to form the hydroxy compound. U. S. Patent 2,229,010 discloses the preparation of certain alkenyl derivatives of biphenohydroquinone by forming a dialkenyl ether of the disodium salt of biphenohydroquinone, and subsequently heating the ether to rearrange it to a nuclear dialkenylbiphenohydroquinone containing a single alkenyl radical on each phenyl ring.

An object of the present invention is to provide a process for the direct conversion of aromatic hydroxy compounds to polynuclear aromatic hydroxy compounds. Another object is to provide a novel reaction between an aromatic hydroxy compound and a compound of the class described below, which reaction results in the formation of carbonate-carbon bonds between molecules of the hydroxy compound substantially in the absence of oxidation oi the hydroxyl groups. Still other objectsandadvant'ages -.will be apparent from the foilowing description of the invention.

In many cases, the reactions of compounds containing a peroxy group (O O-) are characterizedby the chemical changes initiated by 'the decomposition of the peroxy group. Various reactions between aromatic compounds and compounds containingperoxy groups have been investigated. For example, Goldhammer, Biochem. Z. 189 81-87 (1927), reports that phenol reacts with hydrogen peroxide in the presence of ferric sulfate to produce oxidation products, principally pyrocatechol and purpurogallin. Ono and O-yamada, Bull. Chem. Soc.'Jap. 11 132-7 (1936), report that ortho-cresol reacts with hydrogen peroxide in the presence of ferrous sulfate "to produce oxidation products, principally paratoluhydroquinone. Boeskin and Engelbertz, Prac. Acad. Sci. Amstd. 34 1292 (1931), report that in a reaction between phenol and a compound in which the peroxy group'is attached to an organic radical, peroxyacetic acid, a cleavage of the ring occurred to produce oxidation products, principally cis,cis-muconic acid.

We have disovered that when an aromatic hydroxy compound reacts with a compound which contains a peroxy group and which forms among its initial decomposition products hydrocarbyloxy free radicals, i. e., free radicals of the structure RO where R is a monovalent hydrocarbon rad ical, substantially no oxidation occurs and the aromatic hydroxy compound is directly converted to a polynuclear aromatic hydroxy compound. The process provided by the present invention may therefore be described as bringing about a reaction between an aromatic hydroxy compound containing at least one hydroxyl group attached to a carbon atom in the ring, and an organic peroxide in which at least one hydrocarbyl radical is attached to the peroxy group, by creating a mixture of them at the decomposition temperature of the peroxide.

3 Y Aromatic hydroxy compounds which are suitable for employment in the present anesinclude. phenol and its homeless, such as:

The cresols The xylols fl-methyl-ii-tertiary- 2-amyl-4-isopropylphenol 2-butyl-6-cyc1ohenlphenol (3 methyl-2-hydroxyphenybmmanc 2-butyl-6-decylphenol a-methyl-i-cyclohexenylphenol 2-propyl-4-vinylphenol 2-butyl-6-propargylflmol S-tetradecylphenol thenaphtholsandtheirhomologsnehas:

l-decyl-z-hydroxynaphtlnlene l-hydroxy-z-tertiu-y-amylnaphthalene 1-hydroxy-3-hexenyl-naphthalene 1-cyclohexy1-2-hydroxynaphthakne and the po yhydric aromatic hydroay such as:

Resorcinol Pyrosallol Biphenohydroqmnms Naphthylhydroquinone Phenol and its alkyl homologs (which compounds are referredtohytheternuwor a phenol) containing not M tlmn about carbon atoms are a preferred group of reactants for employment in the procem of the invention. whenitisdesiredtoproduceacompoimdsxhibiting particularly strong redneing power, the dialkylphenols of not more than 20 carbon atoms are especially suitable and particularly 300d conversions to individual binuclear aromatic hydroxy compounds are obtained from the 3,6-dislkyl isomers.

Organic peroxides which are suitable for employment in the present process are those which position producm. Organic peroaideainwhichat leastone oftheradicalsattachedtotheperoxy 'groupisahydrocarhylradicalcompriseaeenerally suitable class of peroxide reactants. Illustrative examples of suitable peroxide reactants inelude the dihydrocarbyl peroxides and their analogs in which one hydrocarbyl radical contains polar substituents, such as:

2,2-bis(tertiary-butyiperoxy) butane 2-methylperoxy-2-tertiary-butylperoxy-propane 2 ,2-bis chloro-tertiary-hutylperoxy) pentane Phenyl-bis(tertiary-butylperoxy) methane 2,2-bis(tertiary-butylperoxy) 3 ehloro-pmpane and hydrocarbyl peresters, such as:

Tertiary-butyl perbenaoate Tertiary-butyl perlaurate Di-tertiary-butyldipermalonate Ethyl perbenaoate a 4 "Uheubstitutcdorzanicperoxidesinwhiohat leastonetertiary-alblradicalisattaehedtothe per xr sroup. such as di-tertiary hutyl peroxide,

2,2-bis(tertiary-butylperoxy)butane, and tertiary-butyl perbensoate are particularly preferred reactants, and the di-terflary-alkyl peroxides such as di-tertiary-butyl peroxide are especially suitable for employment in the present process. The term "unsubstituted organic peroxides" is employed to mean peroxides in which the peroxy :roupislinkedsolelytohydrocarbylorhydrocarboyl radicals (radicak of the formula RC(O)-- where R is a hydrocarbyl radical) The temperature at whichthe coupling reaction isconductedmaybevariedorerwidelimiteb! the choice of suitable peroxides, but temperatures from 0' C. to about 200 C. are generally preferable. In general, the reaction proceeds more rapidly at elevated temperatures, and the temperature rinse of from about 100' C. to 150 C. hasbeenfoundparticularlysuitableforthe processoftheinvention. Asthereactionisdependent upon the aromatic hydroxy compound beingcontactedwithfreeradlcalatoconductthe reaction at any given temperature it is necessary to employ a peroxide which decomposes at about that temperature. The decomposition temperature (the recommended temperature ranges for their use) of organic peroxides are determinable properties and are in many cases known to the art. For example, U. 8. Patent No. 2,379,218 describes numerous suitable organic peroxides and the recommended temperature ranges for their use, including:

Diethyl percarbonate to 'Allyl percarbonate 50 to Methyl n-amyl ketone peroxide to I Methyl isobutyl ketone peroxide 110 to 135 Ethyl peroxide 125 to Methyl isobutyl peroxide 130 to Dicyclohexyl peroxide' 150 The decomposition temperature typical peroxides of the particularly preferred class include:

Di-tertiary-butyl peroxide. 100 to 150 The process of the invention may be conducted in substantially any reaction veasel capable of retaining organic liquids and maybe conducted in a batchwise or continuous manner. Either the aromatic hydroxy compound or the peroxide may be empolyed in excess in the coupling reaction. However. it is generally more economical to employ an excess of the hydron compound.

The process of the invention is preferably conducted in the liquid phase. Although substantially any desired reaction pressure may be employed, the use of a reduced pressure can provide but little advantage. Thus, except where a component of the reaction mixture is volatile at the reaction temperature, the use of atmospheric pressure is preferred. Where it is desired to employ as a component of the reaction mixture a compound which is normally volatile at the temperature at which it is desirable to conduct the reaction, the use of superatinospheric pressure is preferred. In general. the peroxides and aromatic hydroxy compounds which are suillciently reactive to provide high yields of product in a short reaction time at a' moderate temperature are those which are normally liquid (compounds which are liquid at about 20? C. under atmospheric pressure), and the employment of such normally liquid reactants, or in general, com

pounds containing not more than 20 carbon atoms, is preferred. However, solid reactants may suitably be employed in the present process by conducting the reaction in amounts of an inert organic solvent (for example, a saturated aliphatic hydrocarbon such as normal heptane, or normal octane, or an aromatic hydrocarbon such as benzene or toluene) sufilcient to dissolve substantial portions of each reactant in a single liquid phase.

The following examples illustrate in detail the application of the process of the invention to the coupling of particular aromatic hydroxy compounds. However, as numerous variations in the reactants and reaction conditions are within the scope of the invention, the invention is not to reactants and reaction conditions recited in the examples.

Example I .Z,6-.'cylen0l Maintaining a solution of 0.84 mole o f, 2,6- xylenol and 0.17 mole of di-tertiary-butylperok ide at a temperature of 130 C. for a period of hours couples the xylenol in accordance with the process of the invention. .The occurrence of the coupling reaction is indicated by the production of only a minor amount of methane. This shows that the tertiary-butoxy free radicals into which the peroxide initially decomposes extract hydrogen atoms from the xylenol to form hydromraryl free radicals and tertiary-butyl alcohol. The product of the reaction can be isolated by filtration or by fractional distillation.

The formation of carbon-tmcarbon bonds with a substantial absence of oxidation of the hydroxyl groups is demonstrated by the fact that 2,6-xylenol treatedlor 48 hours in the above manner produced a crude product melting at 210-18 C. The reported melting point of 3,3,5,5'-tetramethyl-4,4'-biphenohydroquinone is 221 C. The crude product was purified and further identified as the above compound bythe following analysis:

Calculated Found for llHllOl Acetyl value (eq./l g3 0.89 0.83- Carbonyl value (eq./l00 0 0 Percent C 78.8 78.7 79. 3 7. 6 7. 6 7.

Example II.,-2,4-a:ylenol Maintaining .a solution of 0.84 mole of 2,4- xylenol and 0.17 mole of di-tertiary-butyl peroxide at a temperature of 130 C. for a period of hours couples the xylenol in accordance with the process of the invention. The production of only a minor amount of methane indicates the occurrence of the coupling of the molecules. The product is readily removed from the reaction mixture by filtration or by fractional distillation.

Example [IL-Phenol Maintaining a solution of 200 cc. of phenol and 50 cc. of di-tertiary-butyl peroxide at a temperature of between 100 C. and 110 C. for a period of hours couples phenol in accordance with the process of the invention. The occurrence of the coupling reaction is indicated by the production be construed as being-limited to the particular,

of onlya minor amount of methane. The product of the reaction can be removed by filtration or by a fractionalv distillation.

The formation of carbon-to-carbon bonds between more than two. molecules and between polynuclear aromatic. hydroxy compounds.- is demonstrated by the fact that phenol treated-for 40 hours in the above .manner produced a:,gl assf like amorphous solid which was shown by the be a'trimer of the formula following analysis to (CIHAOH) 3, v

' Calculated' Found for. CnHuOt 7 Example IV. 2,4-dimeth1ll-fieisopropulphenol Maintaining a, solution of 0.5 mole or 2,4411- methylfi-isopropylphenol and 0.25 mole of ditertiary butyl peroxide at a temperature of 135 C. for aperiod of hourscouples the phenol in accordancewith the process of the invention.

The occurrence of the coupling'reaction is indicated by the ,evolution of but a minor amount of methane. The productof the reaction can beisolated; by filtration or fractional distillation.

The formation of carbon torcarbon bonds bef tween polyalkylated aromatic hydroxy compounds as well as aromatic hydroxy compounds containing branched side-chains is demonstrated by the fact that 2-,4-dimethyl-fi-isopropylphenol treated in the above manner for 7 hours produced a diphenolic dimer of the formula (CuHuOI-I): as

shown by the following analysis:

7 Calculated Found for 02211300:

Acetyl value (em/ g.) 0. 63 0. 61 Format 0 80.8 81.0 Percent H 0.1 9.2 M. W 321 326 Example V.-'- Resorcinol Maintain'mg asolution of 0.82 mole of resorcinol and 0.41 mole of di-tertiary-butyl peroxide at C. for a period of hours couples resorcinol in accordance with the process of the invention.

The occurrence of the coupling reaction is indi cated by the production of only a minor amount of methane.

Example VL-The use of a dihydrocarbylperozualkane Maintaining a solution of 0.50 mole of alpha naphthol and 0.25 mole of 2,2-bis(tertiary-butylperoxy)butane at a temperature of 90 C. for a period of hours couples the naphthol in accordance with the process of the invention. The occurrence of the coupling reaction is indicated by the production of only a minor amount of methane. The reaction product can be separated from the reaction mixture by filtration or fractional distillation.

Example VIL-The use of a hudrocarbyl pcrester Maintaining a solution of 0.50 mole of mixed cresols and 0.26 mole of tertiary-butyl per-- benzoate at a temperature of 80 C. for a period of hours couples the cresols in accordance with the process of the invention. The occurrence of the coupling reaction is indicated by the production of only a minor amount of methane. The reaction product can be separated from the reaction mixture by filtration or fractional distillation.

4. A process for the production of polynuclear polyhydroxy aromatic compounds whichcomprises heating a mononuclear aromatic hydroxy 8 compound containing at least one hydrcxyl group attached to a carbon atom in the ring with an organic peroxide containing at least one tertiary-carbon atom attached to the peroxy group, to the decomposition temperature oi. the peroxide.

5. A process for coupling aromatic hydroxy compounds which comprises heating an aromatic hydroxy compound containing at least one hydroxyl group attached to a carbon atom in an aromatic ring with an organic peroxide which decomposes yielding hydrocarbyloxy free radicals among its initial decomposition products, at the decomposition temperature.

FRANK H. SEUBOLD, Jr. FREDERICK F. RUST.

WILLIAM E. VAUGHAN.

REFERENCES man The following references are of record in the tile of this patent:

UNITED s'ra'ms PATENTS Number Name Date 2,396,217 Vaughan et a1. Mar. 5, 1946 2,400,041 Dickey May 7, 1946 2,403,709 Dickey. et al. July 9, 1946 2,403,758 Rust et a1. July 9, 1946 OTHER REFERENCES Wieland, Berichte, vol. 54, page 2371 (1921). 

